Strong exciton regulation of Raman scattering in monolayer dichalcogenides

Abstract

The weakly screened electron-hole interactions in an atomically thin semiconductor not only downshift its excitation spectrum from a quasiparticle one, but also redistribute excitation energies and wavefunction characters with profound effects on diverse modes of material response, including the exciton-phonon scattering processes accessible to resonant Raman measurements. Here we develop a first-principles framework to calculate frequency-dependent resonant Raman intensities that includes excitonic effects and goes beyond the Placzek approximation. We show how excitonic effects in MoS2 strongly regulate Raman scattering amplitudes and thereby explain the puzzling near-absence of resonant Raman response around the A and B excitons (which produce very strong signals in optical absorption), and also the pronounced strength of the resonant Raman response from the C exciton. Furthermore, this efficient perturbative approach reduces the number of GW- BSE calculations from two per Raman mode (in finite displacement) to one for all modes and affords natural extension to higher-order resonant Raman processes.

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Cited by in corpus (6)

• Exciton-Phonon Interaction and Relaxation Times from First Principles
• Strongly coupled coherent phonons in single-layer MoS${}_2$
• A library of ab initio Raman spectra for automated identification of 2D materials
• Non-adiabatic exciton-phonon coupling in Raman spectroscopy of layered materials
• Ab-initio wave-length dependent Raman spectra: Placzek approximation and beyond
• Structure, Thermodynamics, and Raman Spectroscopy of Rhenium-Doped Bulk MoS${}_2$ from First Principles